1. Field of the Invention
The present invention relates to a plug-in coupling for connecting a fluid line with a pipe which includes a holding rib extending in circumferential direction. The plug-in coupling includes a pipe piece with a first end portion connectable to the fluid line and a second end portion which can be plugged together with the pipe, wherein the second end portion is connectable to a first coupling ring part of a coupling ring which ring part is connected through elastic holding arms to a non-circular elastically expandable second coupling ring part. The second coupling ring part has locking sections which are distributed over a predetermined circumferential angle range of a circumference of the pipe piece. When the pipe and pipe piece are plugged together, the locking sections slide over the holding rib and expand the second coupling ring part and engage behind the holding rib, wherein the components located between the locking sections of the second coupling ring part are arched outwardly.
2. Description of the Related Art
In a plug-in coupling of this type, known from DE 44 29 498 C1 or EP 1 070 899 A2, FIG. 12, the coupling ring part has an approximately overall elliptical shape. An inwardly projecting locking projection each is integrally formed at the ends of the short elliptical axis, wherein the locking projections engage behind the holding rib when the pipe and pipe piece are plugged together. Consequently, the pipe and the pipe piece are coupled to each other and the pipe is connected to the fluid line which is mounted on the pipe piece. For releasing the coupling, a manual pressure is exerted on the ends of the long elliptical axis directed inwardly toward the short elliptical axis. This deforms the elastic coupling ring part, so that the long elliptical axis is shortened and the short elliptical axis is elongated until the locking projections are disengaged from the holding rib and the pipe piece can be pulled out of the pipe.
This type of uncoupling can be carried out manually in a simple manner, however, this uncoupling is undesirable in many types of applications in order not to spill the fluid which is conducted through the pipe and the fluid line and which may be very hot or environmentally damaging, for example, hot cooling water, oil or fuel of a motor vehicle motor in which, in the case of cooling water, the pipe forms a connecting piece at the radiator and the fluid line forms the cooling water line.
In addition, EP 1 070 899 A2, FIGS. 3a to 3c, disclose forming on a circular coupling ring two to four axial holding arms with radial locking projections at the free ends thereof.